1. Field of the Invention
This invention relates to a postharvest disinfestation treatment to ensure that fruits and vegetables are free of pests so as to meet quarantine requirements. More particularly, the present invention relates to heating fruit or vegetables with hot air under controlled conditions of relative humidity to kill all life stages of quarantine pests present in the commodity without adversely affecting the quality of the commodity.
2. Description of the Art
Certain pests are very destructive to agricultural commodities; thus quarantine restrictions are imposed to ensure that these pests are not disseminated by export of agricultural commodities which may harbor these pests to areas where the pests do not occur. Illustrative of such quarantine pests are tephritid fruit flies (Diptera: Tephritidae) such as the Mediterranean fruit fly, Ceratitis capitata (Wiedemann); the oriental fruit fly, Dacus dorsalis Hendel, and the melon fly, Dacus cucurbitae Coquillett. Fruit flies are among the most destructive insect pests of citrus, deciduous fruits, and vegetables. Tephritid fruit flies are present in Hawaii and have been shown to spread as larvae or eggs in fruits or vegetables shipped from infested areas. Agricultural commodities such as papayas, mangos, avocados, citrus, cucumbers, and bell peppers produced in Hawaii that may be infested with fruit flies cannot be shipped to the mainland U.S. or Japanese markets without quarantine treatment to ensure that the fruits or vegetable are free of fruit flies.
Prior to September, 1984,the standard treatment for papayas was fumigation with ethylene dibromide (EDB). Subsequent to the cancellation by the U.S. Environmental Protection Agency of the use of EDB as a food fumigant, the quarantine treatment that was adopted consisted of selecting papaya fruit of no more than quarter-ripe defined by color standard values measured with a colorimeter and then immersing the fruit in water at 42.degree. C. for 30 minutes followed immediately by a second immersion in water at 49.degree. C. for 20 minutes (Couey and Hayes, Journal of Economic Entomology, 79: 1307-1314 (1986)). The hot-water immersions are used to destroy fruit fly eggs and control postharvest decay. However, the complete treatment is limited because of the ripeness selection and because the water immersions are not sufficiently hot to kill fruit fly larvae inside the fruit.
Another quarantine procedure, called the "vapor heat treatment," uses high-temperature water-saturated vapor to raise the pulp temperature of papaya to 44.4.degree. C. over a 6 to 8 hour period. The fruits are held at the temperature for 8.75 hours, then cooled immediately after the heating phase to below ambient temperature (APHIS, Plant Protection and Quarantine Treatment Manual, Section III, Part 9, Treatment Procedure, 1985). Although this procedure is effective against all fruit fly life stages, the treatment is time consuming and expensive. Also, scalding damage to the fruit may occur.
A modified version of the vapor heat treatment, the "quick run-up treatment," requires heating papayas with saturated water vapor until the fruit center temperature reaches 47.2.degree. C., then immediately cooling the fruits (APHIS, CFR Amendment No. 85-19, Part 318--Hawaiian and Territorial Quarantine Notices). Although this method takes less time, elaborate facilities are still needed and some fruits may be damaged by vapor heat.